Thanks for the response!
We’ll be back in a week to test again – my son has plenty of experience with the “prevo” Rotax throttle, but to be honest, the amount of rolling the throttle he is doing is ridiculous: way, way more than before the kit. After what you wrote, I’m of a mind to start again with 130-125 jet and go from there. Our coach/mechanic also changed the needle position in the carb, to chase the lag. I’ve also been trying to get a hold of another carburetor, to be able to rule that out.
Maxspeed did suggest to check the battery amps and voltage – to try that first before the carb. I’m obviously not an engine tuner, but the three reputable ones that I’ve talked to seem convinced it’s a carburation issue. I’m challenged that we don’t have access to the kart until the testing day, so pretty much we only have that one day to sort it out before the next race…:S